In a typical inkjet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water, an organic material such as a monohydric alcohol, a polyhydric alcohol, or mixtures thereof.
An inkjet recording element typically comprises a support having on at least one surface thereof at least one ink-receiving layer. There are generally two types of ink-receiving layers (IRL's). The first type of IRL comprises a non-porous coating of a polymer with a high capacity for swelling and absorbing ink by molecular diffusion. Cationic or anionic substances are added to the coating to serve as a dye fixing agent or mordant for the cationic or anionic dye. This coating is optically transparent and very smooth, leading to a high gloss “photo-grade” receiver. However, with this type of IRL, the ink is usually absorbed slowly into the IRL and the print is not instantaneously dry to the touch.
The second type of IRL comprises a porous coating of inorganic, polymeric, or organic-inorganic composite particles, a polymeric binder, and additives such as dye-fixing agents or mordants. These particles can vary in chemical composition, size, shape, and intra/inter-particle porosity. In this case, the printing liquid is absorbed into the open pores of the IRL to obtain a print that is instantaneously dry to the touch.
A porous ink jet recording element usually contains at least one ink-receiving layer. The layers may be sub-divided or one or more layers may be coated between the support and an uppermost gloss layer. Usually the gloss layer contains fine particles, for example colloidal alumina or colloidal silica. The layers may be coated on a resin coated or a non-resin coated support. The layers may be coated in one or more passes using known coating techniques such as self-metered coating (roll coating, dip coating, rod or blade coating), premetered coating (slot or extrusion coating, slide or cascade coating, or curtain coating) or air knife coating. When coating on a non-resin coated paper, in order to provide a smooth, glossy surface, special coating processes are often utilized, such as cast coating or film transfer coating. Calendering with heat and pressure may also be used to increase gloss.
Recently, higher speed printing has been demanded of inkjet printers. A problem arises when multiple ink droplets are deposited in very close proximity in a short time: if the porosity of the receiver is not adequate, the drops will coalesce, severely degrading the image quality. The amount of binder in the coated layers is relevant, since if too much binder is present, the porosity of the receiver is diminished, resulting in coalescence, and if too little binder is present, unacceptable cracking is observed. Poly(vinyl alcohol) is known as a very effective binder and is frequently employed in porous inkjet recording media. Even though the amount and type of binder may be selected for maximum gloss and best image quality, better performance with regard to coalescence is desired.
Merkel, et al., in US patent application publication 2005/0013947 disclose the use of a fluorosurfactant in an image receiving layer comprising colloidal silica and poly (vinyl alcohol). When the fluorosurfactant weight is between 0.05% and 3.0%, improvements in gloss, dry time, and coalescence are obtained. Preferred fluorosurfactants are non-ionic, linear, perfluorinated polyethoxylated alcohols. One limitation disclosed by Merkel, et al., is that coating compositions comprising the fluorosurfactants should be coated within a period of twelve hours from the time of addition of the fluorosurfactant to the dispersion, in order to avoid excessive agglomeration of the particles resulting in poor gloss. Instability in a coating composition, such as thickening behavior upon standing, is a problem for manufacturing, the risk being that large amounts of the composition may need to be discarded if an interruption in coating causes the composition to age beyond twelve hours after the fluorosurfactant is added. Another risk is that coating quality may change during a coating event as a function of composition age.